The present invention relates to a heating appliance for air heating, more specifically for heating air that is used for heating the spaces of buildings or similar.
Such heating appliances are used for domestic heating and industrial heating in buildings.
Heating appliances of this type contain a burner, a heat exchanger consisting of a bundle of heat conducting elements that form the primary channels through which the hot flue gases from the burner are guided via inputs that are opposite the burner, and which are connected together to close the secondary channels that are formed between the aforementioned elements and through which the air to be heated is guided along the outside of the elements.
Such heating appliances are known for example in EP 0.706.013.
Thus heat transfer takes place via the walls of the channels between the hot flue gases and the air to be heated.
For such heating appliances, traditionally atmospheric “in-shot” burners are often used whereby the fuel is sprayed centrally into the channels in a gaseous state, whereby the combustion largely takes place in the channels.
These burners have a relatively long flame that extends relatively deeply into the aforementioned channels.
For the combustion in the channels, secondary air at ambient temperature is introduced around the flame, whereby this secondary air also acts as a screen for the channel walls against the hot flame that would otherwise damage these walls.
Such heating appliances with “in-shot” burners ensure a very price-favourable heating solution with many benefits. However, they have the disadvantage that they cause relatively high emissions of harmful substances, such as nitrogen oxides.
The heat exchanger is generally constructed in a modular form from tubular heat exchange elements that are simple and cheap to produce and assemble.
Heating appliances are also known, which, instead of an “in-shot” burner, use a more modern premixed burner or ‘premix burner’ with lower emissions of harmful substances, whereby the fuel is mixed beforehand with the air needed for complete combustion.
In these burners, no secondary air supply is required for combustion.
Premix burners have a much shorter flame, whereby the entire combustion takes place only a few millimetres from the burner and whereby the entire capacity of the flame is thus released in this short distance.
Such premix-burners are not to be used with the known heat exchangers described above without taking additional measures, as the combustion heat is so concentrated that the walls of the heat exchanger would be damaged.
Proposals are known for combining a premix-burner with extra secondary air, as described in U.S. Pat. No. 6,880,548, but these proposals are complex to set up and do not provide the desired result.
The purpose of the present invention is to provide a solution to at least one of the aforementioned and other disadvantages.